Can anyone explain to me why it's OK for the FA to hand me water, soda, etc., but if I try to bring a bottle of the same, purchased on the secure side, onto the plane, it's a problem?

If I'm looking to mix the liquid with something to make a big boom, I think the water the FA hands me will work just as well as the bottle I had planned to bring on board with me.

For that matter, why is OK to get any of the above from the FA, but it's no longer permissible to purchase duty-free liquids on board? Both are liquid, both are on the plane, both can be mixed with something else; makes no sense.

Anyone at TSA ever taken a logic or chemistry class?